A known type of hydraulic braking system for an automobile vehicle is disclosed in Japanese Patent Laid Open No. 6(1994)-171487. The hydraulic braking system includes a first brake circuit and a second brake circuit. The first brake circuit connects the front wheel brake installed on one of the front wheels and the rear wheel brake installed on one of the rear wheels to one of the pressure chambers of a tandem master cylinder. The second brake circuit connects the other front wheel brake and the other rear wheel brake to the other pressure chamber of the tandem master cylinder (diagonal brake circuit).
Each of the brake circuits includes a first solenoid valve and a second solenoid valve (both of which are of the normally open type) which are each installed in a brake conduit connecting one of the wheel brakes to one of the pressure chambers of the tandem master cylinder.
Each of the brake circuits further includes a hydraulic pump driven by an electric motor. An outlet port of each pump communicates with one of the brake conduits connecting one of the solenoid valves to the respective pressure chamber of the tandem master cylinder. Each of the brake circuits further includes orifices which are each installed in a brake conduit connecting one of the wheel brakes to an inlet port of the hydraulic pump.
In accordance with the above described system, the brake pressures in the wheel brakes can be controlled so as to prevent the four wheels from being locked when the wheels are braked (anti-lock control). The hydraulic braking system is also relatively simple in structure so as to be easily manufactured with relatively low cost.
However, the above hydraulic braking system for an automobile vehicle cannot control the brake pressure in the wheel brakes in order to prevent the driven wheels from slipping when the wheels are driven (i.e., the system cannot effect traction control).